n = int(input())
l = list(map(int,input().split()))

l.sort()
s = l[1]-l[0]

if s == 0:
    print("NO")
    exit()
else:
    for i in range(n-2):
        if l[i+2]-l[i+1] != s:
            print("NO")
            exit()
        else:
            pass

    print("YES")